The aim of this research program involves elucidation of the ion permeability mechanisms expressed by primary cells cultured from the embryonic mammalian CNS, from endocrine pituitary and from immune tissues. These mechanisms are considered critical in the physiology and diverse functions of the various cellular phentotypes. Specific lines of investigation include projects on embryonic CNS neurons cultured from spinal and supraspinal regions, clonal and primary pituitary cells and clonal and primary effector lymphocytes as well as their tumor targets. Electrophysiological measurements of excitability are made in membrane patches or in single cells using either low-resistance patch-clamp pipettes or high-resistance microelectrodes for recording. The different assay techniques provide complementary data for characterizing the membrane and cytoplasmic mechanisms underlying ion conductances in these cells. Principal observations this year include the following: 1) cultured hippocampal neurons utilize GABA to signal inhibitory pauses that exhibit a four-fold range in their time course; 2) some GABAergic neurons exhibit a recurrent form of synaptic inhibition that regulates their output; 3) synaptic transmission of GABA signals at GABAA receptors coupled to Cl- channels is depressed by activation of GABAB receptors at pre-synaptic terminals; 4) anesthetic steroids do not share barbiturate block of voltage-gated Ca2+ conductance; 5) putative dopaminergic neurons cultured from the mesencephalon exhibit a distinctive set of excitable membrane properties, an after-depolarization being the prominent and consistent feature; 6) voltage-activated Ca2+ currents differ in FACS-sorted prolactin and growth hormone cells; 7) clonal pituitary cell capacitance rises as cells hyperpolarize to secretagogue; 8) voltage-dependent Ca2+ channels regulate melatonin secretion from chick pineal cells; 9) antigen crosslinking of receptors on clonal immune cells triggers a transient depolarization that can be mimicked by dialyzing cells with inositol trisphosphate and tetrakisphosphate.